Personal computer systems in general and IBM personal computers in particular have obtained widespread use for providing computer power to many segments of today's modern society. Personal computer systems can usually be defined as a desk top, floor standing, or portable microcomputer that consist of a system unit having a single system processor, a display monitor, a keyboard, one or more diskette drives, a fixed disk storage, and an optional printer. These components are usually housed within a metal enclosure, having separable covers. One of the problems with separable covers is the leakage of electromagnetic signals that are radiated or conducted by the electronic equipment inside. This electromagnetic interference (EMI) causes performance reduction to neighboring electronic equipment.
Electromagnetic compatibility (EMC) is the ability of the electronic equipment to perform without suffering or causing performance degradation due to electromagnetic absorption or electromagnetic emissions to its operational environment. Because the trend in personal computer systems is pushing towards faster and higher frequency devices, and therefore higher magnitudes of EMI, the design standards to accomplish acceptable EMC criteria continues to increase. Due to this increasing concern, the Federal Communications Commission (FCC), among other overseas organizations, have set, and are enforcing, regulations to help maintain a clean electronic environment.
In the design of an electronic device such as a personal computer system, to maintain this EMC criteria, it is absolutely necessary to shield the critical inner components with a sealed enclosure of highly conductive material. However, typical of most electronic devices, their packaging incorporates removable covers which, subsequently, creates joints that corrupt the machine seal as well as its EMC integrity. Through studies, it has become known that to maintain the EMC at these joints, conductive contact between the cover and the base enclosure must be made along the entire joint at distances no more than 1/20 of a signal's wavelength. Typically, in today's personal computer systems, this distance is approximately 1 inch.
To overcome this design obstacle, industry has approached this problem with a variety of mechanical fasteners and spring devices. The most reliable, however, the most impractical and expensive, would be a series of screws along the parameter of the joint. This would ensure the required contact but would cause unnecessary hardship to the customer during removal/installation of the covers. The most typical solution used by industry is through the use of finger stock strips or gaskets stamped from highly conductive material. These strips would normally be welded at the joint to a mating edge of the cover or base enclosure and achieve contact through fingers when the covers assembled. Functionally these meet the requirements, however, when the joint is exposed with the cover off, the spring fingers are susceptible to damage and deformation through exposure to the customer. In addition, because the strips are extremely thin to allow for flexibility, they create unsafe conditions for the customer by exposing sharp edges.